1. Field of the Invention
The present invention relates to a glass funnel for a cathode ray tube used mainly for receiving television broadcast signals and for industrial equipments, and a cathode ray tube using such glass funnel.
2. Discussion of Background
A cathode ray tube has a glass bulb which comprises basically a glass panel 1 for displaying images and a glass funnel 2 having a neck portion 5 housing an electron gun 6. The major components of the glass funnel 2 are a yoke portion 4 for mounting a deflection coil 7 and a body portion 3 which is continuous to the yoke portion and extends toward an open end portion for sealing the glass panel 1.
In FIG. 3, reference numeral 16 designates a reinforcing band for maintaining a strength to impact, numeral 10 designates a sealing portion for sealing the glass panel 1 to the glass funnel 2 with a solder glass or the like, numeral 12 designates a fluorescent film emitting fluorescence by the irradiation of electron beams 11, numeral 13 designates an aluminum film for reflecting forwardly light emitted in the fluorescent film, numeral 14 designates a shadow mask for determining the position of irradiated electron beams on the fluorescent film, numeral 15 designates a stud pin for fixing the shadow mask 14 to an inner surface of the glass panel 1, and numeral 17 designates an anode button which is conductive to the outside as the ground so that a high electric potential on the shadow mask 14 by the irradiation of electron beams is prevented.
A symbol A denotes the tube axis connecting the center axis of the neck portion 5 to the center of the glass panel 1, and a symbol B denotes an imaginary reference line indicating the center of deflection. A screen formed in the inner surface of the glass panel by the fluorescent film 12 has a substantially rectangular shape having the tube axis as the central point, and the screen is defined by 4 sides substantially parallel to a long axis and a short axis which cross perpendicular to the tube axis.
The inside of the cathode ray tube is maintained under a high vacuum condition because an image is displayed by irradiating electron beams in the glass bulb. Since the glass bulb has an asymmetric structure unlike a spherical shape and resists a differential pressure of 1 atmospheric pressure between the inside and the outside of it, there is always a high deformation energy in the glass bulb, and it is always in an unstable state of deformation. When a crack is generated in the glass bulb for the cathode ray tube in such state, the crack will extend to release the high deformation energy in the glass bulb to thereby cause destruction. Further, in such a condition that a high stress is applied to an outer surface of the glass bulb, a delayed destruction may be resulted due to the function of moisture in the atmosphere, whereby reliability of the glass bulb decreases.
On the other hand, various kinds of image displaying device other than the cathode ray tube have been proposed in recent years. In comparison with the cathode ray tube with the proposed display devices, the dimension in a direction of the depth is taken as a large drawback. Therefore, an attempt of shortening the dimension in a direction of the depth of the cathode ray tubes has been made. Since the dimension in the depth of the cathode ray tubes is mainly determined by the length of the glass funnel in a direction of the tube axis as understood from FIG. 3, it is effective to reduce the length in order to shorten the depth of the cathode ray tube. FIG. 4 shows a conventional technique proposed to solve this problem wherein the shortening of the depth can be achieved by making the angle of the body portion wide.
However, when the angle of the body portion of glass funnel is made wide as described above, the cathode ray tube becomes flat and has a shape remoter from a spherical shape. Accordingly, the asymmetry in shape of the cathode ray tube is enhanced, and the stress generated in the outer surface also increases. An increased stress will cause a deterioration of safety, if a destruction occurs, and a deterioration of reliability due to a delayed destruction. Although an increase of the stress can be prevented or reduced by increasing the wall thickness of glass as shown in FIG. 4, an increased wall thickness will cause a large increase of the weight, which is another weak point of the cathode ray tube. If the size of a cathode ray tube is increased, the glass bulb becomes inevitably heavy. Accordingly, an increase of the weight due to the wall thickness is a very large problem.
It is an object of the present invention to provide a glass funnel for a cathode ray tube, preventing an increase of stress and reducing the length in a direction of the tube axis by designing well the shape of the body portion, without using a technique of preventing an increase of stress generated in the glass funnel by increasing simply the wall thickness of the body portion.
Further, it is an object of the present invention to provide a cathode ray tube which is safe, light in weight, highly reliable and has a reduced dimension in a direction of the depth and which reduces an increase of asymmetry as a vacuumed envelope and prevents an increase of stress, by assembling the above-mentioned glass funnel.
In accordance with the present invention, there is provided a glass funnel for a cathode ray tube which comprises a body portion having a substantially rectangular open end portion at its one end, a yoke portion formed contiguous to the other end of the body portion and a neck portion connected to the other end of the yoke portion, on an outer side of which a deflection means for deflecting electron beams emitted from an electron gun housed in the neck portion is mounted, wherein a portion of the body portion in the vicinity of the yoke portion is protruded outwardly so that a front end of the yoke portion contiguous to the body portion is located at a position at a side of the open end portion with respect to the portion of the body portion, which is the remotest from the open end portion, and a recessed portion is formed around the yoke portion by the outwardly protruded body portion.
Further, in accordance with the present invention, there is provided a glass funnel for a cathode ray tube which comprises a body portion having a substantially rectangular open end portion at its one end, a yoke portion formed contiguous to the other end of the body portion and a neck portion connected to the other end of the yoke portion, on an outer side of which a deflection means for deflecting electron beams emitted from an electron gun housed in the neck portion is mounted, wherein at least a portion of the yoke portion is recessed to a side of the open end portion with respect to the body portion, and an annularly recessed portion is formed between the yoke portion and the body portion in a circumferential portion of the yoke portion.